Electrostatics does not dictate the slip-stacked arrangement of aromatic π-π interactions.
Chem Sci
; 11(26): 6758-6765, 2020 Jun 05.
Article
em En
| MEDLINE
| ID: mdl-34094127
ABSTRACT
Benzene dimer has long been an archetype for π-stacking. According to the Hunter-Sanders model, quadrupolar electrostatics favors an edge-to-face CHâ¯π geometry but competes with London dispersion that favors cofacial π-stacking, with a compromise "slip-stacked" structure emerging as the minimum-energy geometry. This model is based on classical electrostatics, however, and neglects charge penetration. A fully quantum-mechanical analysis, presented here, demonstrates that electrostatics actually exerts very little influence on the conformational landscape of (C6H6)2. Electrostatics also cannot explain the slip-stacked arrangement of C6H6â¯C6F6, where the sign of the quadrupolar interaction is reversed. Instead, the slip-stacked geometry emerges in both systems due to competition between dispersion and Pauli repulsion, with electrostatics as an ambivalent spectator. This revised interpretation helps to rationalize the persistence of offset π-stacking in larger polycyclic aromatic hydrocarbons and across the highly varied electrostatic environments that characterize π-π interactions in proteins.
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MEDLINE
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En
Ano de publicação:
2020
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Article